Previous rotary engines generally related to the type described in this disclosure may be classified as either curved cylindrical piston or radiating piston type engines. Both types, and particularly the radiating piston type engines, have a rather inefficient combustion chamber with a large surface to volume ratio casing large amounts of unburned hydrocarbon emissions. They also make it difficult to obtain a sufficient range of ignition timing because of the shape of the combustion chamber and the resulting restriction of the location of the ignition means. Furthermore, the curved cylindrical piston type engines are difficult and expensive to manufacture.
The state of the prior art may be ascertained by reference to U.S. Pat. No. 1,298,838 of H. L. Weed; U.S. Pat. No. 3,034,486 of H. L. Buxton; U.S. Pat. No. 3,203,405 of H, Sabet; U.S. Pat. No. 3,302,625 of K. G. Cunningham; and U.S. Pat. No. 3,769,946 of W. A. Scherrer.
U.S. Pat. No. 1,298,838 discloses an internal combustion engine which employs a torus shaped housing accommodating two pairs of pistons, each pair attached to a rotor half. The oscillation of the pistons is accomplished by a mechanism having two two-lobe eccentric gears, four single lobe eccentric gears and six circular gears. However, the arrangement is not practical because it requires very large eccentricity for the single lobe eccentric gears to achieve sufficient amplitude of oscillation. Consequently, the single lobe gears are subject to large variations of loads, a condition which is compounded by the limited space available on the single lobe gears to accommodate a journal or a shaft of sufficient diameter. The output shaft rotates at twice the velocity of the rotor.
The twelve piston rotary engine disclosed in U.S. Pat. No. 3,034,486 employs four oval gears to obtain six oscillations per revolution of the pistons located in a torus shaped housing. The four oval gears are accommodated in a stationary hub of the rotor and transmit the oscillations to the pistons by means of two circular gears and two internal ring gears. In this type of arrangement, the diameters of the oval gears and the maximum diameter of the output shaft are determined entirely by the engine hub radius and not by strength requirements. The output shaft rotates at three times the angular velocity of the rotor.
U.S. Pat. No. 3,203,405 discloses an internal combustion engine employing two pairs of vanes in a drum shaped housing, wherein the relative oscillating motion of the vanes is obtained by an arrangement of three meshing elliptical gears, two circular planetary gears and an internal gear rim. Two of the elliptical gears are planetary gears, engaged with a centrally located elliptical gear. The planetary elliptical gears are integrated with the circular planetary gears and located on a rotating box-like hollow disc. One of the oscillating vane shafts also performs the function of the output shaft which would rotate with a fluctuating angular velocity and therefore requires a large flywheel mass. The sector type vanes radiate directly from the rotor shafts and therefore are subject to high stresses due to the small base area.
The oscillating motion of two pairs of curved pistons disclosed in U.S. Pat. No. 3,302,625 is obtained by a substantially elliptical gear, two eccentrically mounted circular gears and three conventional circular gears. To achieve a sufficient amplitude of oscillation, two of the circular gears in this arrangement should be mounted at high eccentricity causing the same difficulty experienced by the single lobe eccentric gears of U.S. Pat. No. 1,298,838 discussed hereinabove. In addition, output is obtained from one of the oscillating rotor shafts.
U.S. Pat. No. 3,769,946 discloses rotary engines having a number of gear arrangements to obtain oscillation of the pistons. The first embodiment shows an arrangement of four two-lobe elliptical gears, which is also employed in U.S. Pat. No. 3,034,486. One of the other embodiments, employing six two-lobe gears, however, produces no oscillations of the pistons. The embodiments employing a combination of elliptical and circular gears on the power shaft produce generally, an oscillating output rotation, because both pistons have to oscillate so that the moments of inertia forces will be in dynamic equilibrium in accordance with Newton's Third Law. The radiating type pistons have the same disadvantage as those in U.S. Pat. No. 3,203,405. The large concentration of mass at the periphery of the pistons is particularly disadvantageous because of the inertia loads generated by the oscillation of the radiating type pistons.